In the development of specific diagnostic or therapeutic procedures, the use of transfer systems (delivery systems) that allow a possible cell-specific transfer of substances and nucleic acids such as, markers or agents, is of great importance. For this cell-specific transfer systems based on virus-like particles (VLP) have been developed. One of these systems is the VLP from the human polyomavirus John-Cunningham virus (JCV) as described in WO 97/19174 and EP 1270586 B1. Basis of this system is the ability of the VLP to package foreign cargo such as drugs or and nucleic acids instead of the viral DNA. As a VLP still has the ability to specifically recognize cells and to be internalized by the cells the VLP can be used to introduce a cargo of choice into specific cells. However, the VLPs of the state art interact with a very broad spectrum of cells. For certain applications it is desirable to be able to address only specific cell types.
In view of this prior art it is an object of the present invention to improve VLPs for the use as a drug delivery system. In particular it is an object of the present invention to provide means to improve the cell specificity of VLPs.